Coded feedback circuit for railway traffic control



Feb. 3, 1944. THOMPSON I 2,341,300

CODED FEEDBACK CIRCUITS FOR RAILWAY TRAFFIC CONTROL Filed Aug. 18, 1942 4 Sheets-Sheet 1 I I I I I I I I I I I I I I I I I I I I I I I I "L.

INVENTOR flown 1 6L 14. Thompson BY A MVWWZZ HIS ATTORNEY Feb. 8, 1944. A H MP N 2,341,300

CODED FEEDBACK CIRCUITS FOR RAILWAYERAFFIC CONTROL Frequency Selective DU Cir-cu it Feb. 8,19.

H. A. THOMPSON GODED FEEDBACK CIRCUITS FOR RAILWAY TRAFFIC CONTROL Filed Aug. 18, 1942 4 Sheets-Sheet 3 1295011022! Redd (em U12 it I I I l I I I I I LAQQ-Z INVENTOR Howard A. Thompson KFM A 44 HIS ATmRNZ'Y Feb. 8, 1944. H. A. THOMPSON 0 CODED FEEDBACK CIRCUITS FOR RAILWAY TRAFFIC CONTROL Filed Aug. 18, 1942 4 Shets-Sheet 4 g 1L2, a 1' 1E ZNVENIOIZ fibward A. Thompson Patented Feb. 8, 1944 CODED FEEDBACK CIRCUIT FOR RAILWAY TRAFFIC CONTROL Howard A. Thompson, EdgewooiPa assignor to The Union Switch & Signal Company, Swissvale, Pa, a corporation of Pennsylvania Application August 18, 1942,Ser ial No. 455,170

17 Claims.

My invention relates to coded control circuits for use in systems of railway signaling, and it has special reference to the employment by such circuits of the coded feed back operating principle that first was disclosed by Frank H. Nicholson Patent No. 2,021,944 (issued November 26, 1935) and that also is shown by numerous later patents and applications of common ownership herewith.

Generally stated, the object of my invention is to increase the utility and broaden the range of application of coded feed back control circuits of both the track and the line type.

' A more specific object is to organize the apparatus elements of such circuits in a new and improved manner that is alternative to the organization which Assignees Patent No. 2,286,-

002. issued June 9, 1942, to Frank H. Nicholson discloses and claims. I Another object is to provide for such coded feed back control circuits a design wherein the storage potential plus bridging contact protection features of the aforesaid Nicholson form of organization are supplemented by further desirable characteristics not heretofore attainable.

A further object is to render both the "feed back and the master code relays of such circuits highly immune to false operation by foreign and inductive kick back currents that may be present in the circuit conductors.

Astill further object is to provide for direct current track circuits of the frequency code signaling system type an improved feed back design which permits alternating current energy for cab signal control to be superimposed upon the direct current master energy pulses over a supply path which need not include the operating winding of the detector relay.

In practicing my invention I attain the above and other objects and advantages by: (1) using master code and feed back energy pulses which have an opposing polarity relation in the control circuit conductors; (2) Connecting the feed back detector relay to those conductors in multiple (instead of in series) with the master energy source and connecting the master code following relay to those conductors in multiple (instead of in series) with the feed back energy source; and (3) serially including in each of those connections a reactor impedance by which conductor storage energy is prevented from falsely operating the connection-embraced relay.

I shall describe several forms of codedife'ed bat "c'ontrol circuits which embody my invention, and shall then point out the novel features thereof "in claims. These illustrative embodiments are disclosed in the accompanying drawings in which:

Fig. 1 isa diagrammatic representation of a track type of control-ciroui-t that incorporates the improvements of my invention and that is organized "-to form part of an automatic block signalling system having coded feed back approaohlighting control;

Fig. '2shows master and feed back codes which are suitable 'for use'b-y the circuit of Fig. l

Fig. 3 illustrates modified entrance end apparatus for the track circuit of Fig. 1;

Fig. 4 represents modified exit-end apparatus for the same track circuit;

Fig. '5 shows one of my improved track circuits organized into a cab signal only system of automatic block control;

' Fig. 6 shows train-carried cab signal apparatus which may be controlled by the trackway equipment of Fig; 5;

Fig. '7 illustrates modified exit end apparatus for-the trackcircuit of Fig. 5;

Fig. 8 reproduces the cab signal control trac' circuit of Figs. 5-7 together with supplements for the further control and approach lighting of wayside signals;

, Fig. 9 illustrates modified exit end apparatus for the track circuits of Figs. 1,5 and 8; and

Fig. 10 shows how the improvements of my invention may be utilized in a coded trackcir-' cuit scheme of controlled manual bloc'k signaling.

In the several views of the-drawings, like reference characters designate corresponding parts. Referring first to Fig. l, the improved control circuit organization of my invention is there disclosed in association with a coded track circuit system of automatic block signaling for a railway track l2 over which it'will be-assumed that traffic moves "in the single direction indicated by the arrow, or from left toiri'ght "in the diagram. The protected stretch of this track is divided into the customary successive sections by insulated rail joints .3 and the rails of each section formjpart of a track type of control circuit which normally is. capable of transmitting energybetween itsitwo ends but which at times is' rendered incapable or such transmission. 1

' The'ibasic zcomzbimitionpf 1 In this V ew o ;Fig. .1; reference' ch racters II and gI'II respectively designate. the entrance and "the "exit ends or one of these track sections.

This particular section is illustratively shown as being a full signal block in length and its entrance end is guarded by the usual wayside signal 811. Typified by signal $111 at location III is a corresponding device at the entrance end of each of the remaining track blocks in the complete system.

The improved track circuit combination of Fig. 1 is suitable for controlling signal SH and for approach lighting signal SIII without the aid of line wires between signal locations and solely by means of coded energy that is transmitted through the rails of section IIIII.

In the form illustrated by Fig. 1, my improved track circuit combination performs these two functions through the utilization of: (1 apparatus at the section exit III comprising a source of master code energy TB, a coder relay CR having a contact 5 which recurrently applies energy from this source to the section rails l--2 and thereby produces the master code of Fig. 2, the detector relay KR connected in energy receiving relation with the rails, and an approach relay AR which is controlled by the detector relay; and (2) apparatus at the section entrance II comprising a code following track relay TR operated by the master energy pulses that the rails transmit, a source of feed back energy KB, an impulse relay IR having a contact 6 which connects the feed back source with the section rails during each off period (see Fig. 2) .of the received master code, and decoding apparatus H-D which selects the indication of signal $11 in accordance with the rate at which track relay TR follows code.

This rate is, of course, determined by the number of times per minute that the exit end coder relay CR picks up and releases its contact 5 Operation of the coder relay is produced in any one of a number of wellknown manners (not shown in Fig. 1) of, which devices CTl80CTl5--H of Fig. 5 (later to be described). constitute one example. Those elements cause coder relay CR to operate at a high speed or 180 pulse per minute coderate when the section ahead of location III is vacant and at a low speed or '75 pulse per minute code rate when that advance section is occupied.

In either instance, the rails are supplied with mastercode energy in the form of recurring on period pulses that are separated by ofi period intervals. The supply path for each of these pulses extends from the positive terminal of master source TB through a current limiting imped ance 8, front contact 5 of device CR, conductors 9-), the section rails I and 2, and conductors ll-l2 back to the negative terminal of source TB. By each of these master code pulses rail I is made positive with respect to rail 2 and the pulse polarity will herein be designated by the term of positive or given. In the diagram of Fig. 2, each of the master energy pulses has accordingly been represented on the upper side of the base line.

Under vacant conditions Of section IIIlI, these recurring pulses of master code energy are transmitted to the entrance location II. There, each is impressed uponthe operating winding of track relay TR over a path extending from section rail I through conductor M, the winding of relay TR, conductor [5, back contact 6 of device IR and conductors Iii-I1 back to rail 2.

In the form represented, this track relay TR is of the .iamiliar polar biased type the contacts of which pick up only in response to applied winding energy that has the just described normal or positive polarity. Such energy flows current through the relay winding in the direction of from left to right, as shown by the small arrow. Flow of winding current in the opposite direction merely urges the track relay contacts more firmly into their deenergized or released positions.

Looking at the single contact I! that i represented for relay TR, it picks up in response to each pulse of normal polarity master code that reaches relay .TRs winding and releases during each of the off period intervals by which the master code pulses are separated. Application of negative or opposite polarity energy to the relay winding during those off periods is, moreover, inefiective for picking up contact I7.

Through decoding apparatus H-D of wellknown character, track relay TR causes its controlled signal SII to show: (1) clear when the relay is following master code of the 180 or high speed variety; (2) approach when the relay is following master code of the or low speed variety; and (3) stop when the relay fails to follow code. For one illustrative form which such decoding apparatus H-D may take, reference may be had to the entrance end portion of Fig. 8 (later to be described).

By the track circuit elements which have just been described the indication of signal SII thus is selected in customary three indication automatic block manner.

Supplementing these signal control elements are feed back facilities through the medium of which signal SIII may be approach energized without the aid of line wires. These feed back facilities utilize the earlier named devices KB IR at entrance location II and the earlier named devices KR-AR at the exit location III.

Under the control of impulse relay IR, the entrance end source KB supplies the section rails with feed back energy in the form of pulses that recur in step With the o periods of the master code energy which track relay TR receives. In the illustrative form shown, relay IR is of the same polarized type as that shown and described by Herman G. Blosser Reissue Patent No. 21,783. It receives operating, energy from a transformer RT in the exciting circuit of which track relay contact l! operates in well-known pole changing manner.

As long as the winding of this impulse relay IR remains deenergized or receives reverse polarity energy, contact 6 stays released and keeps the operating winding of track relay TR bridged directly across the sections rails. This connection is completed during each on period of the received master code and has already been traced in detail.

At the beginning of each ofi period of the received master code, the accompanying release of track relay contact I! causes transformer RT to supply relay IR with a short pulse of given polarity energy. This energy flows through relay IRs winding in the direction shownby the small arrow and produces a momentary pick-up on the part of contact 6. By each of these pick-ups, sourceKB is connected with the section rails and caused to supply a pulse of feed back energy thereto.

The supply path for each of these feed back pulses extends from the positive terminal of source KB through a current limiting impedance l9, front contact 6 of device .IR, conductors 16-", section. rails 2 and l', and conductdrs'll and back to the negative terminal of source KB. Energy flowing from source KB over the just named. connection makes rail 2 positive with respect to rail I.

This relation being directly opposed to that which results from the earlier described connection of master energy source TB with the section rails, the pulses of feed back energy thus have what will be referred to asa negative or opposite polarity. In Fig. 2, this is shown by feed back pulse representations which are below the base line.

The thus supplied pulses of feed back energy recur in step with the off periods of the master code energy by which the track relay TB is operated; each has the relative shortness indicated by Fig. 2. and terminates before the beginning of the succeeding master code on period; and in being transmitted to the section exit end III, these feed back pulses are impressed upon the winding of the detector relay KR.

This detector relay is a code following device of the polar stick or magnetically toggled type. Flow of current through the relay winding in the direction of from right to left effects a right or reverse positioning of contacts 23-25, while flow of current through the relay winding in the opposite direction effects a left or normal position-- i'ng of those contacts. Once, moreover, the contacts reach either of these positions they there remain continuously until the relay winding is energized in the opposin direction.

In the particular connection shown: (1) each positive or normal polarity pulse of rail-supplied master code energy flows relay current in the first-named direction and thereby opcrates contacts 22-24 to their right position, as is illustrated in full lines. and (2) each windin received pulse of negative or opposite polarity feed back energy flows relay winding current in the second-named direction and thereby operates contacts 23-24 to the left, as shown in dotted lines.

The circuit over which such positive polarity master rail potential energizes relay KR extends from the positive terminal of source TB through impedance 8, front contact 5 of device CR, conductor 9, a reactor 21, the winding of relay KR and conductor l2 back to the negative terminal of source TB. This energifiation occurs during each master code on period and under both vacant and occupied conditions of section lI-III. By it contacts 23-24 are moved' to the right, as earlier stated.

In appearing at the exit location III, each intervening off period pulse of negative polarity feed back energy flows left-to-right current through relay KR over a path that extends from rail 2 through conductor H, the winding'of relay KR, conductor 28, back contact 5 of master coder CR and conductors 9-H) back to the rail I. This current flow takes place during the master code off periods and can occur only when section II-III is unoccupied. By it contacts 23-24 are moved to the left, as earlier stated. I By these contacts 23-26 of detector relay KR. the earlier named approach relay AR is controlled in such manner as to receive pick-up energy when and only when the detector relay is follow ing code. This approach relay AR is of the direct current type and contact 26 thereof is sufiiciently slow in releasing to assure continuous pick-up during code following operation of relay KR.

Any suitable form of approach relay energizing circuit may, of course, be used; In the arrangement of Fig. 1, the approach relay pick-up current originates in course plus-minus,- and is transmitted to the relay through pole changing contact 23 of device KR, an interposed transformer AT and rectifying contact 24 of device KR. In the generally equivalent arrangement which Fig. 4 shows, the transformer AT is dispensed with and pick-up current is transmitted to relay AR directly over contact 23 of device KR.

As arranged in Fig. 1, relay AR can receive energizing current only if the detector device contacts 23-24 are recurrently shifting between their right and left positions. Stoppage of those contacts in either position results in a complete d'eenergization of relay AR and the resultantrelease of its contact 26.

By such release, any desired form of approach energization control may be performed. As illustratively shown in Fig, 1, contact 25 maintains wayside signal SIII disconnected from its lamp lighting source when picked up and completes a signal energizing connection when and only when released.

The non-line-wire approach control combination which has just been described utilizes the coded feed back operating principles of the earlier named Nicholson Patent No. 2,021,944 and its mode of operation will have become more or less apparent from the foregoing description of the entrance end and of the exit end apparatus which the Fig. 1 track circuits utilize.

Under both vacant and occupied conditions of section II-III, the continuously operating coder relay CR recurrently connects the section rails with the exit end source TB and thereby produces a master code of the charactershown in Fig. 2. Under vacant conditions of the section, the energy pulses of this master code are transmitted to the section entrance II where they operate the track relay TR in conventional code following manner.

Through the medium of impulse relay IR, such operation causes the section rails tobe momentarily connected with the entrance source KB during each "off period of the received master code. These connections produce feed back energy pulses which are of the character represented by the lower portion of Fig. 2 and which have a polarity opposite to that of the master code energy pulses.

In being received at the exit location III, these feed back energy pulses aid the master code energy pulses in operating the detector relay KR in the code following manner earlier described. As a result of such operation, approach relay AR is caused to hold contact 26 continuously picked up and thereby to maintain wayside signal SIII normally deenergized.

In the event that a train comes into section II-III, the usual shunting action of its wheels and axles cuts off transmission of master codeenergy to the entrance end track .relay TR and also discontinues transmission of feed back" holds contacts 23-24 continuously in their right or reverse position.

As a result, transformer AT now discontinuesall transmission of pick-up energy to relay AR and causes that relay to release contact 26. Thatrelease, of course, connects wayside signal $111 with its lighting source and thereby causes that signal to display the particular indication which is selected by decoding equipment H-'-D.

This release of the approach relay AR continues until the train moves out of section II--III. When that happens, master code energy is again transmitted to entrance end track relay TR, the section rails are once'more supplied with feed back pulses and those pulses again aid the master code energy in operating the exit end detector relay KR in code following manner. By that operation, the approach relay AR is picked up and wayside signal S111 is thereby restored to its normally inactive condition.

Direct current track circuits of the coded feed back type frequently have to safeguard their feed back energized relays against false operation due to inductive kick back energy which may be generated in the track rails when those rails are shunted. In the track circuit of Fig. 1, such so-generated kick back energy appears in rails I2 at the end of each on period pulse of unidirectional current with which master source TB supplies those rails over front contact of coding device CR.

Direct current track circuits employing detector relays of the type shown at KR in Fig. 1 can experience serious operating difiiculties due to such kick back energy and one early proposal to overcome such difliculties forms the subject of assignees earlier mentioned Patent No. 2,286,002 to Nicholson.

As the specification of that Nicholson patent sets forth in considerable detail, kick back" energy of the type here considered results from the inductance of the track circuit plus the conductance of the rail-to-rail ballast and its effect is to continue for a short interval after each disconnection of source TB from the section rails the flow of current in those rails in the same direction as source TB had established.

When, therefore, the rails of Fig. ls section II--III are shunted by a train each on period pulse of master code current that is impressed upon those rails by source TB may be followed by a kick back energy pulse, which though relatively short, still is long enough to overlap the early portion of the succeeding o code period (see Fig. 2). Off period current due to these overlapping pulses thus may flow from rail 2, over conductor ll, through the winding of relay KR in the direction of from left to right, conductor 28, device CRs back contact 5 and conductors 9-| ll back to rail l If of sufficient magnitude each pulse of such off period kick back current will shift contacts 2324 of relay KR out of their right or master-energy established position into their left position. This response is the same as that which feed back energy received from the section entrance produces and under occupied section conditions it may cause relay KR falsely to follow code.

Assume, for example, that a train has passed location H and is shunting rails I-2 some distance from location III. Under this condition, detector relay KR should hold contacts 23-24 continuously to the right and thereby indicate that section II--III has become occupied. In the absence of counteracting means the just described master kick back energy may prevent such holding and cause relay KR to continue to follow code even though no feed back energy is being transmitted thereto.

In order to guard against such false operation of detector relay KR the exit end apparatus of Fig. 1 makes use of a reactor 21. This reactor was previously named in tracing the circuit over which relay KR receives on period current pulses from master source TB. In addition to forming a part of that circuit, reactor 21 keeps relay KRs winding connected with rails I2 during the early portion of each master code off period when coding contact 5 shifts from its front to its back position.

Such connection enables advantage to be taken of the inductivecharacteristics of relay KRs winding plus those of the reactor 21. Such characteristics result in the generation of a local kick back voltage at the end of each passage of unidirectional current from source TB through the reactor and relay winding. That generation is, of course, produced by the collapse of magnetic flux which accompanies each disconnection of the named elements from source TB.

Upon each of those disconnections: (l) theenergy stored in the circuit of the section rails I--2 tends to flow through the winding of relay KR' from left to right; and (2) the energy of selfinductance in relay KRs winding plus that in reactor 21 tends to continue the flow of current through the winding relay KR in the opposite or right-to-left direction.

. These currents directly oppose each other and by choosing the magnitude of the windings plus reactors kick back current to slightly exceed that generated in the rails, the contacts 23-24 of relay KR are effectively held to the right following each disconnection of master code source. TB from the shunted rails.

In practice reactor 21 may take the form of' an adjustable element which is set at such a value as to produce the relation just expressed. Should relay KRs winding itself be capable of producing all of the counter inductive effect that is needed, then the reactor 21 may be-replaced by a resistor (not shown) or other impedance. When employed as is device KR at location III of Fig. 1 most code following relays of commer-1 cial design are, however, found to require some. counter inductive supplement and for this reason use of the represented reactor for element 2'! ordinarily will be preferred.

When organized as at exit location III of Fig. 1 this reactor element 21 exerts its kick back: neutralizing effect during the initial or early portion only of each off code period. This is because each off period closure of coding device CRs back contact 5 by-passes element 21' and thus leaves only the winding of relay KR to oppose the reactive effect of the rail circuit.

In practice, however, this by-passing of reactor 21 by back contact 5 is found to detract but little or nothing from that reactors effectiveness as a neutralizer of rail kick back current. Such current rises to its highest level immediately after coding contact 5 leaves its front position at the master code pulse end and it is found to attain that level before contact 5 reaches its back position. All during this interval reactor 21 is exerting its full neutralizing efiect. By the time, in consequence, that contact 5 reaches its back position that rail kick back" current either is completely overcome or is so greatly diminished that the reactive effect of relay KRs winding alone readily holds it in check. V

In the improved entrance end organization:

which I. have shown at location II in Fig. 1, use, is made of a comparable reactor 29. actor keeps relay TRs winding connected withthe section rail during the master code 01152,

This re--.

periods when relay IRs contact 6 is picked up. Its function is to safeguard track relay TR against false response due to inductive kick back" energy that may be present in the track rails immediately following the feed back pulse ends.

As previously explained relative to Fig. ls exit end reactor 21, such kick back energy results from the inductance of the track circuit plus the conductance of the rail-to-rail ballast; it is likely to be present in the rails of a shunted track section at the end of each direct current energy pulse that is impressed thereon; and when so generated its effect is to continue for a short time after each disconnection of the D.-C. source from the rails the flow of rail current in the same direction as was established by that source.

If such feed back kick back energy persists after device IRs contact 6 has reconnected track relay- TR to the section rails, it will, therefore, flow current through relays TB in such direction as falsely to pick the relay up. Under certain operating conditions of track section II-III, such false pick-up is highly objectionable-and the purpose of added reactor 29 is to make it impossible.

In achieving'the stated pick-up prevention by feed back "kick back energy, advantage is taken of the inductive characteristics of relay TRs windings plus those of reactor 21 and their effect in generating a local kick back voltage at the end of each application of direct current to the relay winding. The stated effect is produced by the collapse of magnetic flux which accompanies each disconnection of the winding and reactor from feed back source KB. Reactor 2.) establishes for relay 'I'Rs winding a connection through which each pulse of trackway energy from that source KB flows current through the winding of relay TB in the direction of from right to left.

As earlier explained, such current flow is inefiective for picking up relay TR and thus it does not interfere with the desired code following response of that relay to the master code energy pulses which are applied thereto. It does, however, render the relay immune to false pick-up by feed back kick back energy which may be applied thereto over device IRs back contact 6 following disconnection of source KB from the section rails.

Upon each of these disconnections: (1) the section rails l-2 tend to flow through the winding of relay TR a feed back kick back current in the direction of from left to right; and (2) the energy of self-inductance in relay 'IRs winding tends to continue the flow therethrough of current in the opposite or right-to-left direction.

These currents directly oppose each other and by choosing the magnitude of the windings plus reactors kick back current to slightly exceed that generated in the rails, relay TR is effectively held released following each disconnection from the rails of feed back source KB.

In practice reactor 29 may take the form. of an adjustable element which is set at such a value as to produce the relation just expressed. Should relay TRs winding itself be capable of producing all of the counter inductive effect that is needed, then the reactor 29 may be replaced by a resistor (not shown) or other impedance. As, however, most code following. relays of commercialdesign are found to require some counter inductive supplement, use of the represented reactor for element 29 will ordinarily be preferred.

When organized as at entrance location II of Fig. 1 this reactor element 29 exerts its kick back neutralizing effect only from the instant that impulse relay IRs contact 6 leaves its front position at the fed back pulse end until the slightly later instant that contact 6 reaches its back position. This is because each back closure of contact 6 by-passes element 29 and thus leaves only the winding of relay TR to oppose the reactive effect of the rail circuit.

In practice, however, this by-passing of reactor 29 by back contact 6 is found to detract but little or nothing from that reactors effectiveness as a neutralizer of rail kick back current. Such current rises to its highest level immediately after the impulse of relay contact 6 leaves its front position and it is found to attain that level before contact 6 reaches its back position. All during this interval reactor 29 is exerting its full neutralizing effect. By the time, in consequence, that contact 6 reaches its back position that rail kick back current either is completely overcome or is so greatly diminished that the reactive effect of relay TRs winding alone readily holds it in check.

In addition to assuring that the master track relay TR and the feed back detector relay KR will not falsely respond to inductive kick back energy received from the section rails, the complete coded feed back track circuit combination of Fig. 1 also protects the two relays just named from unsafe response: (1) in the event that contact 5 of master coder CR fails to interrupt the rail supply path from master source TB before establishing the rail connecting path for detector relay KR or fails to interrupt the detector relay path before establishing the master source path; and (2) in the event that contact 6 of impulse relay IR fails to interrupt the rail connecting path for master track relay TR before establishing the rail supply path for feed back source KB or fails to interrupt the feed back supply path before establishing the track relay circuit.

In both instances, this bridging contact protection is a direct by-product of the opposing polarity relation between the pulses of master code energy from exit end source TB and the pulses of feed back" energy from entrance end source KB. This relation has already been de'-- scribed in detail and is clearly indicated by the diagram of Fig. 2.

Looking first at location IIIs combination of exit end devices CR-TB-KR, assume that contact 5 of relay CR is incorrectly adjusted or builds up so that it engages its front and back points at the same time. Such a condition causes master source TB to be continuously connected both with the rails of section II-III and with the winding of detector relay KR. That relay, quite obviously, now holds its contacts 23-24 continuously to the right and at theentrance location II track relay TR is held continuously picked up. Both of these stoppages of code following operation simulate the effects which a shunting of the section rails |-2 produces and neither is in any way unsafe.

Looking next at location IIs combination of entrance end devices IR-KBTR, assume that contact 6 of relay IR is incorrectly adjusted or builds up so that it engages its front and back points at the same time. In that event, feed back source KB is continuously connected both with the section rails |-2 and with the winding of the track relay TR. As a result of that connection, relay TR is held continuously released. As in the preceding instance of contact bridging, this effect is on the safe side.

A further advantage of the Fig. 1 track circuit organization resides in its inherent tendency to keep rail storage potentials at a level far below that required to falsely operate either of the rail connected relays TR and KR. As is well known, each pulse of applied trackway energy, particularly in a direct current system of the type here shown, causes to be built up between the section rails a storage potential which persists for a short time after the energy ceases to be applied.

When, as in prior track circuit combinations of the type which the earlier named Nicholson Patent No. 2.286.002 typifies, the master and the "feed back energy pulses have a coinciding polarity relation, the build up efiect tends to be cumulative and the level of storage potential may then build up and substantially delay release of the track relay contacts on termination of each impulseof master code.

In'my improved organization, however, the opposing polarity relation (see Fig, 2) of the master and feed back pulses directly counteracts this tendency of storage potential build-up. Each pulse of positive polarity master code energy is followed by a negative polarity pulse of feed back energy which, in turn, is followed by a positive pulse of feed back energy, and so on. In consequence, storage potential of neither polarity has a As has already been seen, the improved coded feed back control circuit combination of my invention is characterized by: (1) use of master code and feed back energy pulses which have an opposing polarity relation in the control circuit conductors; (2) connection of the feed back detector relay KR to those conductors in multiple with the master energy source TB and connection of the master code following relay TR to those conductors in multiple with the feed back energy source KB; and (3) serial inclusion in those connections of reactors 21 and 29 by which conductor kick back" energy is prevented from falsely operating relays KR and TR.

As might be expected, the earlier described Fig. 1 illustrates only one of a number of possible apparatus connections by which the just stated features may be provided. In Figs. 3 and 4, other possible organizations of the entrance and of the exit and elements arerespectiveiy represented.

In the modified entrance end organization of Fig. 3-, the kick back neutralizing reactor 29 is included in rail conductor l4 (instead of in conductor ll as in Fig. l) the feed back source KB is interposed between rail conductor I! and impulse relay IRs front contact 6 (instead of jin ing with conductor 20 as in Fig. 1) and conductor l5 connects relay IRs back contact 6 with the left terminal of master track relay TR (instead of with relay 'IRs right terminal as in Fig. 1).

Despite these modifications, the entrance end apparatus of Fig. 3 has operating characteristics which duplicate those of Fig. 1. Each positive or given polarity pulse of master code energyconductors M and 20, back contact 6 of device IR, conductor l5, the winding of relay TR and conductor ll back to rail 2.

As in Fig. 1, the energy impressed bytrans former RT upon impulse relay IR due to this pick-up by relay TR'fails to move contact 6 from its released position. In consequence,"that contact keeps the feed back source KB disconnected from the section rails during the full fon period of the received master code.

As in Fig. 1 also, the release of track relay TR which accompanies each mastercode off period causes transformer RT to supply impulse relay IR with a'short pulse of pick-up energy. Responding to this pulse, relay IR picks up contact 6 and'thereby: (1) inserts reactor 29 in the track relay circuit; and (2) connects feed back sourceKBwith the section rails. v

Because of this connection, the rails now are supplied with an ofi period pulse of feedback energy over a path extending from the'positive terminal of source KB through current limiting impedance I9, conductor II, the track rails 2 and I, conductors l4 and 20 and, front contact 6 of device IR back to the negative terminal of source KB.- As in Fig. 1, this so-supplied feed back ener y pulse has a negative or opposite'polarity and continues for the relatively short duration represented in Fig. 2. Within the master code off period which initiated the pulse, relay IR releases and terminates the pulse by disconnecting source KB from the section rails.

Following this disconnection, relay IRs contact 6 sets up a shunt path around reactor 29 and thus conditions track relay TR for reception of and response to the succeeding on period pulse of given polarity master code energy. When that pulse is received there is started a sequence-of actions which duplicate those just described.

As in Fig. 1, the reactor 29 of Fig. 3 renders track relay 'I'R immune to false pick-ups by rail kick back energy that follow each disconnection of feed back source KB from the track circuit. Inasmuch as the Fig. 3 organization confers this immunity in a manner fully equivalent to that. earlier explained for the Fig. 1 organization, no further description of this action is here believed necessary.

Referring now to Fig. 4, the exit end apparatus organization there shown will be seen to bear to the location III apparatus of Fig. 1 a relation comparable to that just explained between' the entrance end organization of Fig. 3 and the location 11 apparatus of Fig. 1.

In Fig. 4, detector relay KRs reactor 2! is included in. rail conductor ll (instead of in onductor ID as in Fig. 1) the master energy source TB is interposed between rail conductor l0 and coder relay CRs front contact 5 (instead of being joined with conductor l2 as in Fig. 1) conductor 28 joins relay CRs back contact 5 with th left terminal of detector relay KRs winding (instead of with the. right terminal as in Fig. 1); and the detector relay controlled approach relay AR receives pick-up current directly overrelay KRs left or reverse contact 23 (instead of through an interposed transformer AT as in Fig. 1)

Despite the several detail changes just named, the exit end apparatus of Fig. 4 has operating characteristics which are equivalent to those earlier explained for the corresponding elements of Fig. 1.

Each pick-up of coder relay CRs contact 5 causes source TB to supply the section rails with an on period pulse of normal polarity master code energy. The pulse supply path extends from th positive terminal of source TB through current limiting impedance 8, conductor [0, track rails I and 2, conductors Il--l2 and front. contact 5 of device CR back to the negative terminal of source TB.

During this master code on period, source TB also flows current through the Winding of relay KR over a path extending from the sources positive terminal through impedance 8, the winding of relay KR, reactor 2?, conductor I2, and device CRs front contact 5 back to the sources negative terminal. The direction of this current flow is from right to left and it causes relay KR to operate contact 23 to the right or reverse position illustrated.

In moving to the released position at the master code on period end, device CRs contact 5 disconnects source TB both from th section rails and from the winding of detector relay KR. Such disconnection establishes a master code off period andv connects the Winding of relay KR directly with. the section rail l--2. Contact 23 of the now deenergized relay KR continues to occupy the right position shown, and is shifted away from this position only when negative or opposite polarity feed back energy is received by relay KR.

Under vacant conditions of the track section behind location III, such reception occurs (see Fig. 2) early in each so-definedmaster code off period. By the then received pulse of opposite polarity feed back energy, relay KR is energized over a path extending from track rail 2 through conductors H!2, device CRs back contact 5, conductor 28, the winding of relay KR and com ductor I!) back to track rail i The flow of feed back current through relay KR is from left to right and by that flow contact 23 is operated to the left or normal position. As in Fig. 1, this contact positioning continues until relay KR receives another given polarity pulse of master code. energy. Contact 23 stays to the left, therefore, even after the off period pulse of feed back energy has been terminated.

In picking up at the cit period end, device CRs contact l: reinserts reactor 21 into relay KRs energizing circuit and reconnects master source TB both with the section rails and with relay KRs winding. Such reconnection establishes another master code on period and starts a sequence of operations which duplicates that just explained. By the first of those operations relay KR shifts contact 23 back to the right or reverse position illustrated.

Under vacant section conditions, therefore, detector relay KR at Fig. as location III is caused to position contact 23. to the right during each on period pulse of master code energy that is supplied to the section. rails and to position contact 23 to the left during each off period pulse of feed back energy that is received from those rails. ,As in Fig. i. such shifting is effected by the opposing polarity relation between the master and feed back energy. During such code following operation. by relay contact 23, Fig. is approach relay AR is supplied with code step pulses of pick-up energy over a path extending from the positive terminal of a local control source through the Winding of relay AR and back tothe negative terminal of the control source.

As in Fig. 1, contact 25' of relay AR is made sufuciently slow releasing to bridge the master code on periods and by the recurring pulses of approach relay pick-up energy just named,

contact 26 is. accordingly held continuously picked up. Such a positioning of the contact indicates that the track section to the rear of location III is vacant and. that off period pulses of negative polarity feed back energy are being received from entrance apparatus which may duplicate that shown at location II in either of Figs. 1 or 3.

When a train comes into the section to the rear of Fig. as location III, the shunting action of its wheels and axles cuts oil the just named feed back energy transmission and thereby deprives detector relay KR of all negative polarity energization. As in Fig. l, the relay continues to receive positive pulses of master code energy and accordingly holds contact 23 continuously to the right. Because of this holding, the approach relay AR. is now deprived of all pick-up energy and that. relays contact 26 accordingly releases. By that release, an occupied condition of the track section is indicated.

By Fig. 425 reactor 2'! the detector relay KR is rendered immune to false operation by rail kick back energy that may result from each of coding contact Es interruptions in the connection of the master energy source TB with the track circuit. Inasmuch as the actions incident to this immunity are the same as those previously explained for the exit end organization of Fig. 1, no further description thereof is here deemed necessary.

In addition to this kick back energy immunity the exit end. apparatus organization of Fig. 4 ofiers protection against foreign rail current which is comparable to that offered bythe corresponding organization of Fig. 1. If the foreign current makes rail 1- continuously positive. with respect to rail 2, the effect thereof on detector relay KR is to urge contact 23 to the right. Under vacant section. conditions, this effect may prevent the negative polarity feed back pulses from operating contact 23 to the left and in that event approach relay AR will release contact 26 in the same manner as were the section occupied. Under occupied conditions of the section, the negative polarity foreign rail energy merely aids master source TB in holding relay KRs contact 23 to the right and therefore does not disturb the normally released positioning of approach relay ARs contact 26.

The just stated safe response to foreign rail energy of negative polarity is effected not only by the exit end. apparatus of Fig. 4. but also by the exit end apparatus of Fig. 1'. There a continuous positioning of detector relay contacts 23-24' either to the right or. to the left eifects the continuous release of approach relay ARs contact 28.

With either of those arrangements, however. some false operation might be experienced if the foreign rail energy continuously makes rail 2 positive with respect to rail I. In that event, the detector relay KR of both Figs. 1 and t might conceivably follow code at a time when the extreme entrance end II of the section was shunted by a train. As the train approached exit location III, however, such false operation would soon ceasedue to the reduction in foreign rail potential which would necessarily accompany the advancing raili shunt. v

Mention has already been made of an earlier developed coded feed back track circuit organization which is disclosed and claimed by assig-nees recently issued. Patent No. 2,286,002 to Nicholson. In that Nicholson organization: (1)

the exit end master source TB utilizes a series connection with the detector relay KR for supplying on period pulses of master code energy to the section rails; (2) the entrance end feed back source IBicorresponding to element KB hereof) utilizes a similar series connection with the track relay TR for supplying off period pulses of feed back energy to the section rails; and (3) the polarity relation in each of these connections is such that current from the connection-included source flows through the winding of the connection-included relay in a direction which is opposite to the flow of winding current that is produced by relay operating energy received from the opposite end of the section.

In the case of Nicholsons polar biased track relay TR, at the section entrance, the just stated relation is necessary to prevent that track relay from being falsely picked up by the off period pulses of rail current that the feed back source flows through that relays winding. Similarly, in the case of Nicholsons polar stick detector relay KR. at the section exit, the named polarity relation is imperative in order that the on period pulses of master rail current which exit end source TB flows through that detector relays winding will operate the relays polar contacts to a position opposing that to which they are operated by the off period pulses of feed back energy that are received from the section entrance.

Because of the requirements just explained, the Nicholson combination must utilize master and feed back energy pulses which have a coinciding polarity relation. In certain instances, as a previous portion of this specification has already indicated, such polarity coincidence is not entirely desirable in that it permits rail storage potential to cumulatively build up instead of being held in check as in the staggered polarity organization of my present invention.

As compared with the Nicholson organization, therefore, the improved coded feed back track circuit combination herein disclosed offers the important advantage of utilizing a staggered polarity relation between the master and feed back energy pulses and of thereby minimizing the storage potential that tends to build up between the track rails as a result of coded direct current energy application thereto.

Cab signal only organization of Figs. 5-6

A further difificulty with the Nicholson organization is encountered when attempts are made to provide. for the control of train-carried cab signals. In accordance with present preferred signaling practice, such provision requires that alternating current energy be superimposed upon the direct current master pulses which are applied to the section exit-and which recur at a rate that is distinctive of traffic conditions in advance of the application point.

In the earlier discussed Nicholson organization these direct current master energy pulses are impressed upon the section rails over a series connection with the detector relay KRs operating winding and any alternating current cab signal control energy that is superimposed upon those master pulses must, therefore, also flow through the detector relay winding. When alternating current cab signal control energy is supplied to the section rails through the winding of the feed back detector relay, this relay must be of a type which will not respond to this energy. This preasetsoo vents the use of a sensitive relay at this point and therefore limits the length of track section over which the track circuit may be operated.

The improved coded feed back track circuit organization of my invention overcomes this shortcoming and provides for the supply of alternating current energy to the section rails over a circuit which does not include the feed back detector relay in series therewith. One preferred manner in which such facilities may be combined with my earlier explained basic form of coded feed back track circuit organization is shown by the diagram of Fig. 5.

In that diagram there is reproduced: (1) at entrance location II the entrance end apparatus of Fig. l modified to utilize a decoding transformer DTI in place of the impulse relay transformer RT and to dispense with the wayside signal S11; and (2) at the exit location III the exit end apparatus of Fig. 1 modified to show the driving facilities for master coder relay CR, to dispense with the wayside signal S111, and to include in the rail supply circuit of direct current master source TB a track transformer TT through which energy from an alternating current source BC of 60 cycle per second or other commercial carrier wave frequency is at proper times supplied to the section rails.

The track circuit organization of Fig. 5 is intended for use in a frequency code block signaling system of the cab signal only type wherein all signal indications along the wayside are dispensed with and traflic movements are governed solely through the medium of traincarried apparatus of the conventional character represented in Fig. 6.

By that figure there is shown train-carried cab signal circuits which are of conventional frequency selective character and which embody principles and apparatus that are more completely described by Paul N. Bossart Patent No.

1,773,472 dated August 19, 1930.

In these Fig. 6 circuits, use is made of the usual pick-up windings 32-33 mounted on the 1000- motive front; an amplifier 35 that strengthens the energy which these windings inductively received from the track rails |2; a code following master relay MR which is energized through a transformer 36 by a measure of the output of this amplifier and which responds to each pulse of received trackway energy having the alternating current character that is supplied from source terminals BC of Fig. 5; a decoding transformer DT which is supplied with code step pulses of exciting current over a pole changing contact l'la of the master relay; frequency selective circuits DU into which the decoding transformer feeds its output energy; decoding relays HR. and DR which receive pick-up current from these frequency selective circuits; and a cab signal CS having a plurality of indicating units which are selectively energized under the control of the decoding relays.

The elements just named cooperate in such a way that: (1) when the master relay MR follows alternating trackway code of the 180 pulse per minute variety both of the decoding relays HR and DR pick up and light (over front contacts 38-49) the green or clear indication lamp G of the cab signal CS; (2) when the master relay follows alternating current trackway code of the pulse per minute variety only the first decoding relay HR picks up and front contact 38 plus back contact 39 then complete the 'lightingcircuit for the yellow or".approach'i-n dication lamp Y of the signal; and '(3) when the master relay ceases to follow code and holds contact Ila continuously in-one position both of the decoding relays release and light (over back contacts 3839) the red or stop indication lamp R-of the cab signal.

The trackway organization of Fig. supplies the rails .of section II--III with the alternating current energy which is required to operate the cab signalapparatus of Fig. 6 and it does this without in any way interfering with the desired orsafe operation of the exit end detector relay KR.

While the track transformer TT of this Fig. 5 organization might at all times'be connected with the alternating current source terminals B-C, it is preferable that this transformer energizing connection be completed onlywhen a train comes into the section to the rear of the transformer location. For so approach! energizing transformer TT, use is made of a contact 4! carried by the approach relay AR. Under vacant conditions of section II-III this contact is picked up and it then by-passes the primary of transformer TT and thereby reduces the impedance offered by that transformers secondary to the flowtherethrough of direct current from master code source TB.

Under occupied conditions .of section 11-111, relay ARs contact 41 is released and alternating current from source B-C then continuously excites transformer TT over a circuit extending from terminal B through back contact 4|, conductor '42, the primary of transformer TT and conductor 43 back to terminal 0. As a result of this excitation, transformer T1 superimposes upon each of the direct current master energy pulses from source TB the component of alternating current energy earlier described as being suitable for train-carried cab signal control.

As long as any part of the train continues in section IIIII, each pick-up of master coder relay CRs contact 5 causes the section rails to receive this alternating current energy from transformer TT. In the illustrative arrangement of Fig. 5, the supply path extends from the lower terminal of TTs secondary through conductor 44, track battery TB, impedance 8, front contact 5 of device CR, conductors 9 track rails I-2 and .conductors lI-l2 back .to the upper terminal of TBs secondary.

Upon passage of the train out of the section II--III, master code energy from the directcurrent source TB once more reaches and operates entrance end track relay TR. That operation causes impulse relay IR .to connect feed back source KB with the section rails during the master code ofi periods and as a result of those connections exit end detector relay KR once more follows code and picks up approach relay AR. By that pick-up contact 4! disconnects transformer TT from source B-C and thereby removes all alternatin current energy from the section rails.

As in the exit end organization of Figs. 1 and 4, the detector relay KR at Fig. 5s exit location III receives current from direct current source TR during each on period of pulse of master code energy which that source supplies to the rails. This, reception is by Way of a kick back neutralizing reactor 2'! and in each of Figs. 1, 4-5 the on period current so impressed upon relay KR serves to return that re- :lays contacts to the rightin order that each received pulse of feed back current will shift them to the left.

By Fig. 5s reactor 21 the detector relay KR, '5 -is rendered immune to false operation by rail kick back energy that may result from each of coding contact 5s interruptions in the connection of the master energy source TB with the section'rails. Inasmuch as the actions incident to this immunity are the same as those previously explained for the exit end organizations of Figs. 1 and 4, no further description thereof is here deemed necessary.

'In order that Fig. 5s coded pulses of alternating current energy will not objectionably affect 'the detector relay KR, the kick back neutralizing reactor 2-7 in'that relays energizing circuit may be supplemented by an inductance 30 which =wl'1ile-freely'passing unidirectional current from EZJlsource'TB excludes to a'la'rge extent the flow of alternating current from source BC. Use of this added inductance 30 is, however, optional since it is possible to design the direct current detector relay KR'in such manner that its contact 23willnot follow the A.-C. frequency revers- -ing polarity' current which the relay receives through reactor 2'! from the cab signal control source B-C.

For selecting in accordance with advance traffic conditions the rate at which master coder 'relay CR operates, the complete track ciruit organization of Fig. 5 utilizes the usual code detecting relay H. As shown at exit location III, this relay has a contact 46 which when picked up connects coder device CRs driving circuit with contact 180 of a high speed code transmitter 'CTI80 'and which when released connects the same driving circuit with contact 15 of a low speed code transmitter CT15. Under the condition first stated, relay .CR produces a master code made up of 180 energy pulses per minute and under the condition last stated device CR produces a master codef made up of 75 energy pulses per minute. I

This exit end relay H is associated with the section in advance of location III and it is controlled in the manner shown at section II-IIIs entrance location II. As long as track relay TR follows code of either the 180 or the '75 pulse per minuterate, decoding transformer DTl supplies (over a rectifying contact 18) relay H with winding current which holds contact 46 continuously picked up. Upon failure of track relay TR to followcode, however, this winding current supply is discontinued-and contact 46 then releases.

From the foregoing'descri-ption of the coded track circuit apparatus of Fig. 5 and of the traincarried cabsignal equipment of Fig. '6, it will be apparent-that a three indication system of automatic block cab signal control may be provided by equipping each of a plurality of consecutive track sections with this Fig. 5 apparatus and arranging that the entrance vend relay H of each section determine (by means of contact 46 as shown at location III) the rate of pulse recurrence of the direct current plus alternating current (when needed) master code energy that is supplied to the exit end of the rear adjoining section.

Trains equipped with the cab signal apparatus of Fig. 6 thus set up in customary three indication automatic block manner their own followin protection in passing through such a signaled stretch of track. I

Referring to Fig. '7, I have there shown one alternative organization for the code producing and selecting facilities of Fig. s location III. In it Fig. 5s code repeater relay CR. is dispensed with and the circuits over which sources TB and TT supply energy to the section rails are carried directly over contacts I80 and 15 of code transmitters CTIBD and CT'IB. V

As in Fig. 5, selection between those code transmitter contacts is effected by contact 46 of relay I-I. When that relay is picked up (as shown) transmitter contact I80 performs the functions of Fig. 5s repeater contact 5 and when relay H is. released transmitter contact 15 performs the functions of Fig. 5s repeater contact 5.

In either instance, each pick-up of the selected transmitter contact connects sources TB--TT in energy applying relation with the section rails l2 and each released positioning of the select- ,ed'transmitted contact transfers the rail connection directly to the winding of detector relay KR. In consequence, the modified exit end apparatus of Fig. 7 operates in a manner which'is the full equivalent of that earlier explained for the exit end apparatus of Fig. 5.

Wayside and cab signal organization of Figs. 8-9

By extending the trackway apparatus organization of Figs. 5 and '7, the cab signal control functions thereof may be supplemented by indications displayed by wayside signals S. Fig. 8 shows one preferred form which such wayside supplements may take.

The coded feed back track circuit diagram of that figure: 1) reproduces at entrance location II the entrance end apparatus of Fig. 5 and additionally shows a wayside signal SII plus a code distinguishing relay.v D plus signal control contacts 38- -39 carried by relays H-D; and (2) reproduces at exit location III Fig. 5s exit end apparatus modified in accordance with Fig. 7, and additionally shows a wayside signal SIII plus indication selecting apparatus H-D therefor plus an approach lighting contact 26 carried by relay AR.

This exit location III apparatus of Fig. 8 supplies the rails of section IIIII: (l) with 180 pulse per minute master code energy when' the section in advance of location III is vacant; and (2) with 75 pulse per minute master code energy when that advance section is occupied.

At Fig. 8s entrance location II: (1) reception of the 180 master code energy causes track relay TR to produce pick-up on the part of both of the decoding relays H and D and thereby places wayside signal SII at clear; (2) reception of the 75 master code energy produces pick-up on the part of decoding relay H only and thereby causes signal SII to show approach; and (3) absence of received master code energy allows decoding relays H and D both to release and thereby places signal SII at stop. The just described response of relay D to 180 code energy only results from an inclusion of a frequency selective unit IBDDU in the circuit over which the relay receives pick-up energy from decoding transformer DT2.

The mode of operation of Fig. 8s complete track circuit combination will have become apparent from: the earlier given descriptions of that combinations several organizations of individualapparatus elements.

Trains equipped with cab signaling apparatus of the type shown in Fig. 6 receive on board their leading vehicles automatic block indications due to transformer TTs supply of alternating current energy pulses during all occupied conditions of section II-III; moreover, trains passing through the signaled stretch further receive from the wayside signals S automatic blockindications of conventional three indication character. Both the wayside si nals S and the cab signal supply transformers 'IT are approach energizedthrough the medium of my improved feed back apparatus organization.

Referring to Fig. 9, the improvements of my invention are there shown as being applied to an organization of exit end apparatus which is'alternative to that shown at location III in Fi 8. Here the feed back detector relay takes the form of a double-winding device KRX of the polar biasedtype which is organized in a manner more completely described by assignees Patent No. 2,275,838 to Herman G. Blosser andv which picks up only in response to a flow through wind ing 52 of current in the direction of from left to right.-

By this Fig. 9 organization use is made of a master coder CR having two contacts 5 and 59 which operate in synchronous relation with respect to each other. Controlling the driving circuit of this relay CR are code transmitter facilities of the type shown at location III in Fig. 5.

When contacts 5 and 50 are picked up, master energy source TB supplies the section rails (not shown in Fig. 9) with a pulse of master code energy. The supply circuit extends from the positive terminal of source TB through conductor. 48, front contacts 5 and 50 in parallel, conductors 49 and Ill, the section rails I and 2 (see Fig. 8), conductor ll, current limiting impedance 8, the. secondary of transformer TT and conductor 44 back to the negative terminal of source TB.

When device CRs contacts are released the connection just traced is interrupted and the pick-up winding 52 of detector relay KRX then is bridged across the section rails. This bridg ing is over a circuit that extends from rail 2 (see Fig. 8) through conductor ll, relay KRIS winding 52, conductor 54, back contact 5 of device CR, and conductors 53, 49 and I0 back to rail I (again see Fig. 8). Over that circuit each pulse of feed back energy that is transmitted to location III (from entrance end apparatus of the character shown at location II in Fig. 8) picks up this detector relay KRX at the beginning of the master code 01f period during which the pulse is received.

A further effect of the release of coder relay CRs contact 50 is to complete an energizing circuit for a stick winding 56 of detector relay KB! and for the pick-up winding of the approach relay AR. In addition to back contact 56 of device CR, this circuit includes a front con} tact 51 of detector relay KRX and it is organized in a manner disclosed and claimed by assignees Patent No. 2,272,789 which issued to Herman G. Blosser on February 10, 1942.

In the illustrative form shown, this circuit derives its energy from master code source TB and when completed it extends from the positive terminal of that source through conductor 48, device CRs back contact 50, conductor 58, the winding of approach relay AR, front contact 51 of relay KRX, conductor 59, the stick winding 56 of relay KRX and conductor 60 back to the neg ative terminal of source TB.

Such completion is possible only when relay acetone -RX s; pick d up; by; n-.. fff: period. pulse; f; feed back energy received ;over the section;rails from apparatus of the character-,-sho wn at ;lo.ca tion II-inFig. 8. Such reception, inturn; is possible only when theassociated' track sectionisunoccupied; Under that condition, relay becomes picked up during each off period; of;

the master code which relay GR- of Fig. 9pmduces.

By the circuit just traced asincluding back.

contact to of device CR and; front contact of relay KRX, the approach relay. AB is energized during the master code off periods, and,

each pick-up of detector relayKRiisprolonged for the-full duration of the off code period during which it occurs.

With this description of prior artstructure as a background, the improvements of; my;invention which I have applied toFig. 9 will now. be considered. These improvements-reside in the inclusionbetween rail conductor l9 and the right terminal of relay KPUXs pick-unwinding 52 of a reactor 2'! by which the detector relay KRX. is rendered immune to false pick-up. by master kick back energy thatmay begeneratedin the section rails l and ,2 (see Fig. 8) upon each dis.- connection of master source TB-therefrom.

AsqshoWn-in Fig. 9, this reactor 21 is supplemented byan inductance 30 thatis occasioned by the alternating current supply transformer TT which comes into actionwhenever the associated track-section (again see Fig. 8) becomes occupied. In situations, where the direct current master. code energyis not sosupplemented by-alterhating current cab signal energy, this inductance 30 may bedispensed with.

Underoccupied conditions ;of the track section with which Fig. 9 apparatus is associated, transmissionof feed back energy to relay KRXs pickupwinding 52 is discontinued and it is desired that relay KR! then not pick up. The earlier mentioned master kick back ener y-has incertain installations been observed to cause difliculty by virtue of. flowing through'the winding; 52-at. the oil period beginning current which causes relay KRX falsely to operate eventhough the track section is occupied.

. By'including reactor 2'! in that windings en'- ergizing circuit, I effectively prevent this falseoperation and do this in a manner closely com parable to that earlier explained. forthe corresponding reactors 2i and 290i the earlierpresented figures.

The earlier mentioned Blosser Patent No.

2,275,838 omitted all connection betweenconduc-.

tors id-and 54. under picked-up conditionsof. relay CRs coding contact 5. No energy fromrmastersource TE was, therefore, permitted- 130 reach windingiiZ during the on code periods.-

By providing reactor 2'! (and inductance 39:. when required) 1' cause current fromv masterv of KRXs polar biased type, it is ineffective for picking up contact El. Such pick-up requires a flow of current through winding52 in the die ion of f om; leftrfi ht. s; ow ib r-th Feed back pulses received; fromapparatus of the character shown;at'location-,II:

in Fig, 8 produce this pick-up direction flows The current-flowing inthe opposite direction from source TB during each master, code on period causes windingtzto .generate alocal inductive-kick back potential upon interruption of that currentat the on period end-\- T is. local kickback current tendsto flow. from'right; to'left and it directly opposes the rail kickback energy which reaches the winding 52 atzthe same on period end;

description thereof. is; deemed-necessary,

The-track circuitcombinatz'on of Fig. 10-

Referring, to Fig, 10, comparable. kick back}? neutralizing means arethere shown in ass ocia. tion with the track circuitportions. of a con-,- trolled manual block, signaling scheme wherein it becomes desirable to relay coded track energy.-

- over long distances.

In the particular arrangement illustrated, only two track sections VI .V Ia and VIa--.-VII.v are.

shown. At location VII, a,code,transmitter CTI. recurrently, picks upandreleases contact 5.whenever, a,controlling switch 64.i s closed. At location, VI, similarly, acode transmitter CKlrecurrente. ly picksupandreleases-a Contact 6 whenever a. controlling switchfi'l therefor is closed. In the controlled manual block system earlier men:

tioned, only oneofswitches 64 and. 61 isclosed at. any particular time.

Under conditions of the represented closure of switch 54, and. the opening of switch 6], each pick-up of transmitter CTlscontact 5-.causes a source TBi at location VII to pick up a track; re-

layTRl at location VIa. over a circuitextending fromthe positive terminal of sourceTBl through an impedance 8, CTls front contact 5, conductors 9, and Ill, sectionra-il I, conductors M. and 65, back contact 5!; of device KRI, conductor 1c, the'windingof relay TRI, conductors. inland Il,

section rail 2, and conductors. I l-l2 back to thenegative terminal source. TB I Each release of codingcontact 5 at location VII interruptstheconnection just traced and bridges the section rails, I- 2 directly across the winding of .a track relay KRZ. Included in this bridgingconnection is back contact. 5 and a conductor 2.8.

At the cut location VIa, relay TR accordingly.

picks upand releases. its contact 69in step with the pick-ups and releases of transmitter CTls contact '5. at location VI. By relay TRis contacts!) there. is recurrently completed a circuit over. which a source T132. at location VIo; picks up a track relayTIRZ. atlocation VI. This pick.- up circuit 1 ext-ends. from the. positive terminal, of source T332. through conductor H, front contact 69hr device TRI', conductors 9a and Hl section rail la, conductors Ma and l'il; back, contact 6;, of device CKI, conductor 80, the winding oi relay TRZ, conductor Ha, rail 2a, conductor Ha, and impedance lzbacktothe negative terminal of source T132.

Each release of track relay TR! atv location; VIaJnterruptsthe circuit just traced andbridgcs;

the section rails lc-2a directly across the windnig of a track relay KRI'. Included in this bridging connection is relay TRls back contact 68 and a conductor 13.

I At location VI relay TRZ accordingly picks up and releases its contact 16 in step with the pickups and release: (1) of relay 'IRls contact 69 at location We; and (2) of transmitter C'I'ls contact at location VII. By this code following action of contact 16 any desired control function peculiar to manual block signaling may be performed.

Under other conditions wherein location VIs switch '61 is closed and location VIIs switch 65 is opened, transmitter CKI recurrently picks up and releases its contact 6 and transmitter CT! keeps contact 5 continuously released. Each such pick-up of CKls contact 6 causes a source KBI at a location VI to pick up track relay KRI at location VIa over a circuit extending from the positive terminal of KBI through conductors l3 and Ila, section rail 2a, conductor Ila, the winding of relay KRI, impedance 29, conductor Hla, section rail la, conductors Ma and I1, CKls front contact 6, and impedance 19 back to the negative terminal of source KBI Each release of coding contact 5 at location VI interrupts the connection just traced and bridges the section rails lat-2a directly across the Winding of relay 'IRZ. Included in this bridging connection is back contact 6 and the earlier named conductor 80.

At the cut location VIa, relay KR! accordingly picks up and releases its contact 66 in step with the pick-ups and releases of transmitter CKls contact 6 at location VI. By relay 'I'Rls contact 68 there is recurrently completed a circuit over which a source KBZ at location VIa picks up track relay KRZ at location VII. This pickup circuit extends from the positive terminal of source KBZ through impedance 82, conductor ll, section rail 2, conductor l l, the winding of relay KRZ, conductor 28, back contact 5 of device CTI, conductors 9l0, section rail I, conductors l4 and 65, relay KRls front contact Eli and conduotor 83 back to the negative terminal of source KB2.

Each release of track relay KR! at location VIa interrupts the circuit just traced and bridges the section rails [-2 directly across the winding of track relay TRI. Included in this bridging connection is relay KRls back contact 66 and the earlier named conductor 10.

At location VII relay KRZ accordingly picks up and releases its contact 86 in step with the pickups and releases: (1) of relay KRIs contact 66 at location V111; and (2) of transmitter CKls contact 6 at location VI. By this code following action of contact 86 any control function peculiar to manual block signaling may be performed.

From the diagram of Fig. 10 it will be noted that each of the there represented four track relays TRI, TRZ, KRI and KRZ is of the polar biased type the contacts of which pick up only in response to a flow through the relay winding of current in the direction of from left to right, as shown by the arrow. As in the case of device TR of each of Figs. 1, 3, 5 and 8, flow of winding current in the opposite direction merely urges the track relay contacts more firmly into their deenergized or released positions.

From Fig. 10 it will further be noted: (1) that the energy received by each track relay TR! and TRZ from the parallel-connected sources KBZ and KBI at the relay location produces this opposite direction of current flow and hence is inefiective for picking up that TR relay; and (2) that the energy received by each track relay KRI and KRZ from the parallel-connected sources TB2 and TBI at the relay location similarly produces relay current flow in a direction ergy that may be generated in the track rails at the end of each of the energy pulses that is applied at the relay location. Location VII's relay KRZ will serve to illustrate. With respect to it the possibility of false kick back" response occurs each time that device CTls contact 5' from track section disconnects source TBI VIaVIIs rails I 2.

Due to the inductive properties of those rails plus the conductance of the rail separating bal last, such disconnection is accompanied by a tendency for kick back current to continue to flow in the rails in the same direction as source TBI produced while coding contact 5 was picked up, Upon that contacts release, therefore, this kick back current may falsely pick up track relay KRZ over a path extending from rail 2 through conductor II, the KR2 winding, conductor 28, C'I'I s' back contact 5, and conductors 9 |0 back to rail I.

For preventing such false pick-up on the part of each of Fig. l0s track relays KRZ-TRI- KRlTR2, I include in the rail-connecting circuit for each relay a reactor 29 which corresponds to and performs the same functions as the similarly identified element in each of Figs. 1, 3, 5 and 8. Here, as in those earlier figures, reactor 29 establishes for the track relay winding a con-- nection through which each pulse of rail energy applied at the relay location flows current through the relay winding in the non-pick-up direction.

In the case of location VIIs relay KR2, the path for this current flow extends from the positive terminal of source TBI through impedance 8, CTls front contact 5, conductor 9, reactor 29, the winding of relay KRZ and conductor I2 back to the negative terminal of source TBI. ineffective for picking up relay KR2, this rightto-left flowing current builds up in the relay winding and in the reactor a magnetic flux by which an energy of self inductance is later generated.

Upon the subsequent release of location VII's coding contact 5: (l) the section rails l2 tend to flow through the winding of relay KRZ a kick back current in the direction of from left to right; and (2) the then generated energy of self inductance in relay KR2s winding and. in reactor 29 tends to continue the flow therethrough of current in the opposite or right-to-left direction.

These currents directly oppose each other and by' While the obvious "identity of the immunity producing structures and operations no' further discussion of these remaining .impedances is deemed necessary.

Summary Although the several improvements oi'my invention have been shown and described as'forming parts of codedcontrolcircuits of the track type, it will be obvious thatthese improvements are not restricted to track circuits but that" they also have utility when applied to control'circuit combinations of any other'form wherein'the'conductors lose their normal energy transmitting capability under certain conditions only.

Thus, instead of being track rails asshownfthe control circuit conductors l"2 may also f take the form of line'wires which connect masterenergy supply andfeed back receiving equipment (see devices at location III in each of Figs. 1, 4,-.5,"7, 8, 9) at one end of the circuit,

with master energy receiving and feedback energy supply equipment (seede'vi'ces TR-IR '.KB at location IIin each (smears, ;8) atthe other end of the circuit.

When used in control circuits ofthe line conductor type just described, each of theimprovements herein disclosed will'func'tion in "exactly the same manner as when used with'thetrack type of control circuits'thatare herein illustrated. My invention is, therefore, one of broad utility and is not restricted to the specific forms of application that'I have shown by way of'illustra tion.

From the foregoing description of Figs. 1 to '10, therefore, it will be seen that I have made important contributions to control circuit combinations of the coded feed back class. In '.par-' ticular, I have increased the utility and broadened the range of application of coded feed back control circuits of both the'track andthe line type; I have organized the apparatus ele ments of such circuits in a new and improved mannerthat isalternative to "the organization which assigneesPatentNo, 2286.002 toFrank H. Nicholson discloses and claims; I have'pro-vided for such coded feedback control circuits a'd'esign wherein the storage potential plus bridging contact protectionfeatures oi the aforesaid Nicholsonformof organizationare supplemented by further desirable characteristics not here-t0- fore attainable; Ihave rendered both the "feed back and the master code relays of suchcircuits highly. immune to false operation by foreign and inductive kick back currents that may be present in the circuit conductors; and I have provided for direct current track circuits of the frequency code signaling system type an improved feed back design which permits alternating current energy for cab signal control to be superimposed upon the direct current master energy pulses over a supply path which need not include the feed back detector relays op erating winding.

Although I have herein shown and described only aiew forms of coded control circuits which embody my invention, it'is understood that various changes and modifications may be made therein within the scope of the appended claims without departing 'from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. In combination, asectio-n'of track that in cludes first and second trafiic rails, means at the exit end of said section for'supplying said section rails with master code energy in tlie for rn errecurrin'g' on: period pulses 'that' are separated by ofi "period intervals and that' are' of" a given polarity which makes said first r a'il positive with respectto said second, means-located at the entrance end of said sectionandoperatedby'the there-received pulses of said master i code energy for further supplying-said rails' with' puls'es of feed back 'energy that recur in step with saidniaster code to periods "and that are of an opposite polarity which "makes said second rail po'sitive with"respect 'to -said first, a code following detector relay at 1 saidsection s exit end connected across said rails and having a contact which i'espends to each rail-supplied -pulse-of said given polarity master code ener by moving to a first position and I which responds to each 5 rail-tra nsmitted pulse of Said 'o'ppo'site polarity feed "back energy by 'moving to-a second: position, and tramc governing apparatus "controlled *by said detector relay contact and distinctively responsive-according as that-contact isor is'n'ot repeatedly shifted between "its-saiwfirst and second positions.

2. Incombi n ation,- a-section-of track that includes first'ahdsecond traific 'rails;-meansincluding a coding contact at the exit end of said sec tion for--supplying s'aid section rails with master cod'e energyin the" form of recurring pulses that are fof a given polarity which 'm'ak'es s'aid first-rail positive with respect to said-second, means located at' the entrance e'nd ofsaid section and operated byth'e there receivedpulse'sbf said master code energy for further 'supplying said railswith pulseso'f feedback energy that recur in step'with said master code off periods and that are of an opposite polarity Which m'akes "said s'e'cond 'r'ail positive with respect to said-first; a code following detector relay at saidsections exit end having an operating winding which is connected in parallel with said rails' andb'eing provid'ed with a contact which responds to "eachwinding-recei'ved pulse of s'aid 'give'n polarity "mastercode energy by moving to a first -position and which responds to each winding-received pulse of said opposite polarity feedback energy by moving-Eton second position, an impedance serially included in said connectionto'limit the flow-through said relay winding of current that is" due'to'said on periodpul'ses of master codeenergy, means governed by said coding contact for by-passing'said impedanceduring said master code off periods whereby to render it ineii'e'ctiveiduring received pulses of said feed backienergy, and traiiic governing apparatus controlled by *said J detector "relay contact and distinctively responsive accord ing as that coritactis oris"notib'eing'repeatedly shifted between its saidifirst andsecond"positions.

3. In combination, a :control circuit th'at' 'includesrfirs't and second conductors which normal 1y are capable 'oftransl'nitting energy between given. and opposite end's'of the circuit 'butwh'ich at times "are "rendered incapable of such/transmissionym'eans at the give'nkend of said circuit for "supplying said ccnductors' with master c'ode energy'in the form of recurring fon tpericd pulses that are separated "by fofi period intervals and 'that are or a 'pos'itive poiarity'which makes said "first conductor positive -with respect t'osaid second, means-locatedi'atitheopposite end of said' circuit and operated by thethere received pulses r said master ceae energy icr further supplying said condiict fee'd back erierg'y that remlarity which makes said second conductor positive with respect to said first, a code following detector relay at said given circuit end connected in energy receiving relationwith said conductors and having a contact which responds to each of said conductor-supplied pulses of positive polarity master code energy by moving to a first position and which responds to each of said conductor-transmitted pulses of negative polarity feed back energy by moving to a second position, and signaling apparatus controlled by said detector relay contact and distinctively responsive according as that contact is or is not being repeatedly shifted between its said first and second positions.

4. In combination, a control circuit that includes first and second conductors which normally are capable of transmitting energy between given and opposite ends of the circuit but which at times are rendered incapable of such transmission, means at the given end of said circuit for supplying said conductors with master code energy in the form of recurring on" period pulses that are separated by off period intervalsand that are of a positive polarity which makes said first conductor positive with respect to said second, means located at the opposite end of said circuit and operated by the there received pulses of said master code energy for further supplying said conductors with pulses of feed back energy that recur in step with said master cod fofi periods and that are of a negative polarity which makes said second conductor positive with respect to said first, a code following detector relay at said given circuit end having a winding which is connected across said conductors to receive operating energy therefrom and being provided with a contact which responds to each winding-received pulse of said positive polarity master code energy by moving to a first position and which responds to each winding-received pulse of said negative polarity feed back energy by moving to a second position, and signaling apparatus controlled by said detector relay contact and distinctively responsive according as that contact is or is not being repeatedly shifted between its said first and second positions.

5.- In combination, a control circuit that includes first and second conductors which normally are capable of transmitting energy between given and opposite ends of the circuit but which at times are rendered incapable of such transmission, means including a coding contact at the given end of said circuit for there supplying said conductors with master code energy in the form of recurring on period pulses that are separated by off period intervals and that are of a positive polarity which makes said first conductor positive with respect to said second, means located at the opposite end of said circuit and operated by the there received pulses of said master code energy for there further supplying said conductors with pulses of feed back energy that reour in step with said master code off periods and that are of a negative polarity which makes said second conductor positive with respect to said first, a code following detector relay at said given circuit end having an operating winding which is connected in parallel with said conductors and being provided with a contact which responds to each windingrreceived pulse of said positive polarity master code energy bymovin to a first position and which responds to each winding-received pulse of said negative polarity feed back energy by moving to a second position,

an impedance serially included in said connec tion to limit the flow through said relay winding of current that is due to said on period pulses of master code energy, means governed by said coding contact for by-passing said impedance during said master code off periods whereby to render it inefiective during received pulses of said feed back energy, and signaling apparatus controlled by said detector relay contact and distinctively responsive according asthat contact is'or is not being repeatedly shifted between its said first and second positions.

6. In combination, a control circuit that includes first and second conductors which normally are capable of transmitting energy between given and opposite ends of the circuit but which at times are rendered incapable of such transmission, means at the given end of said circuit for supplying said conductors with master code energy in the form of recurring on period pulses that are separated by "off period intervals and that are of a positive polarity which makes said first conductor positive with respect to said second, a code following relay at the opposite end of said circuit having a winding which is connected with said conductors and being provided with a contact which responds to each winding-received pulse of said positive polarity master code energy by moving to a picked-up position and which occupies a released position when said winding either fails to receive positive polarity energy or has negative polarity energy impressed thereon, means governed by said relay contact and effective during master energy Produced code' following operation thereof for further supplying said conductors with feed back energy in the form of pulses that recur in step with said mas ter code off periods and that are of said negative polarity which makes said second conductor positive with respect to said first, a code following detector relay at said given circuit end connected in energy receiving relation with said con ductors and having a contact which responds to each of said conductor-supplied pulses of positive polarity master code energy by moving to, a first position and which responds to each of said conductor-transmitted pulses of negative polarity feed back energy by moving to a second position, and signaling apparatus controlled by said detector relay contact and distinctively responsive according as that contact is or is not being repeatedly shifted between its said first and second positions.

7. In combination, a control circuit that includes first and second conductors which normally are capable of transmitting energy be tween given and opposite ends of the circuit but which at times are rendered incapable of such transmission, means at the given end of said circuit for supplying said conductors with master code energy in the form of recurring on period pulses that are separated by oiT period intervals and that are of a positive polarity which makes said first conductor positive with respect to said second, a code following relay at the opposite end of said circuit having an operating winding which is connected in parallel with said conductors and being provided with a contact which responds to each winding-received pulse of said positive polarity master code energy by moving to,,a picked-up position and which occupies a released position when said winding either fails to receive positive polarity energy or has negative polarity energy impressed thereon, means including an impulse device governed by said relay 2, SZL QOO contactand-effective during master energy produced "code following operation therefior further supplying said conductors with feedback energy in the "form of pulses that recur in step with said master code on periods and-that are of said negative polarity which makessaid-secnd conductor positive with respect to said first, animpedance seriallyincluded in said conductorto relay winding connection to limit the fiow throughsaid-winding of current that is due'to said "off period "pulses of feed back energy, means governed by said impulse device ior bypassing said impedance during each on period of 'the received master'code whereby to render it inefiective during each received master code energy pulse, a code followingdetector relay-at said given circuit end connected in energy receiving-relation with said conductors-and having-a contact which'responds to each "of said condu'ctor supplie'd pulses of positive polarity master code energy-"by moving to-a first position and which responds to each of said conductortransmitted pulses of negative polarity feed back energy "by "moving to a second position, and signaling apparatus controlled by said detector relay contact 'and distinctively responsive according as that contact is or is not-being repeatedly shifted between its said first and second positions.

*8. "Ina coded railway signaling-system; in combination, a section of railway track, a code following track relay having its winding connected across*the section-rails atone end of 'the'track section, a feedback detector relay at the other end of said track section having one terminal of its winding connected "to "one terminal of the winding of a reactor, the other terminalo'f the detector relay Winding being connected by -a-first conductor to one track rail and the other terminal of the reactor windingbeing connected by'a second conductor to the other track rail of said track section, said detector relay being-0f a type the contacts of which are moved from a first to a second position when and only when energy flows through the relay winding in a given direction, a coding device having a'contact continuously actuated between a first and a second position, said coding device contact being efiective when in its first position to-connect a track battery across said conductors to thereby cause energy to be supplied fromsaid battery to the section rails and to also cause to be suppliedto the detector relay winding through the reactor energy which flows through the winding of said detector relay in the reverse of said given direction, the reactor being proportioned so that on interruption of the circuit of the track battery the energy supplied from the reactor to the detector relay prevents operation of the detector relay by energy supplied theretodue to inductive discharge of the track circuit occurring on interruption of the circuit of the track battery, and means associated with the track relayand operative when the coding device contacts are in their second position to supply to the detector relay winding over the track rails feed back energy'which flows through the winding of said detector relay in said given direction.

9. In acoded railway signalingsystem, in-combination, a section of railway track, a code following track relay having its winding connected across the section rails at one end of the track section, a feed backdetector relay at :the other end of the track section having its windin connected across the section rails, said detector relay beingsof a 'type t'he contact of which-are moved from-a first to a-second position when and only when "energy flows through the :relay winding in a given direction, 'acoding device:havinga contact continuously actuated zbetw'eena first and a second position, said coding 'device'contact'ibeing efiective when in its first positionto connect a track battery across the section rails andthe winding of said detector relay in multiple so that energy from the track battery flows through the winding of said detector "relay in the reverse :of said given direction, the circuit over'which'energy is supplied from the track battery to :the "detector relay being of relativelyhigh inductance so that on interruption of the circuit *of the track battery energy continues to flow temporarily in the circuit of the detector relay'winding in the reverse of said given direction and istof such magnitude as to'preventioperation of the relay by energy supplied thereto due to inductive discharge of the track circuit occurringnn interruption of the circuit .ofithe track-battery, and means associated with the track relayzand operative when the coding device contactsiaresin their second position to supply to the detector relay winding over the section rails feedback energy which flows through the winding *ofrsaid detector relay in said'given direction.

10. In a coded railway signaling system, .in combination, a section of railway track, a code following track relay having its winding connected across the section rails at. one end of the track section, a feed back detector relay at the other-end of the track section having itswinding connected across the section rails, said *detector relay being of a type the "contacts of which are moved from a first to a second position when an'd only when energ flows through the relaywinding in a given direction, a coding device having a contact continuously actuated between afi-rs't and a second position, said coding device contact being effective when in its first position to connect a track battery across the section rails and the Winding of said detector relay in multiple so that energy from the track battery flows through the winding of said detector relay in the reverse of said given direction, the circuit over which energy is supplied from the'track battery to the detector relay including in series therewith an inductive Winding so that on interruption of'the circuit of the track battery the inductive discharge from said inductive winding temporarily maintains flow throughthe detector relay winding in the reverse of said given direction energy of such magnitude as to prevent operation of the relay by energy supplied thereto due to inductive discharge of the track circuit occurring on interruption of the circuit of thetrack battery and means associated with the track rela and operative when the coding device contacts are in their second position to supply to the detector relay winding over the track rails feed back energy which flows through the winding of said detector relay in said given direction.

11. In a coded railway signaling system, in combination, a section of railway track having a first and a second track rail, a code following track relay at one end of said tracksection having its Winding connected across the section rails in series with .a first reactor with the first terminal of said relay winding connected to said first rail'and the second terminal of said relay winding connected to said second rail, said track relay being of a type the contacts of which aremoved' from .-a I first to a second position when and i only when cnergy'flOWs through the lre'lay winding from its first to its second terminal, a code following detector relay at the other end of said track section having its winding connected across the section rails in series with a second reactor with the first terminal of said relay winding connected to said first rail and the second terminal of said relay winding connected to said second rail, said detector rela being of a type the contacts of which are moved from a first to a second position when and only when energy flows through the relay winding from its second to its first terminal, a coding device having a contact continuously actuated between a first and a second position, said coding device contact being effective when in its first position to connect a track battery across the section rails in multiple with the detector relay winding and said second reactor with the positive terminal of said battery connected to said first track rail, and means effective on movement of the track relay contacts to their first position to momentarily connect a feed back battery across said section rails in multiple with the winding of said track relay and said first reactor with the positive terminal of said battery connected to said second track rail, each of said reactors being effective on interruption of the supply of energy from th associated battery to momentarily maintain flow of energy through the winding of the associated relay and thereby prevent operation of the relay by energy supplied to the relay due to inductive discharge of the track circuit on interruption of the supply of energy from the battery at that end of the track section.

12. In a coded railway Signaling system, in combination, a section of railway track having a first and a second track rail, a code following track relay at one end of the track section having its winding connected across the section rails with the first terminal of said relay winding connected to said first track rail and the second terminal of said relay winding connected to said second track rail, said track relay being of a type the contacts of which are moved from a first to a second position when and only when energ flows through the relay Winding from its first to its second terminal, a code following detector relay at the other end of the track section having its winding connected across the section rails with the first terminal of said relay winding connected to said first track rail and the second terminal of said relay winding connected to said second track rail, said detector relay bein of a type the contacts of which are moved from a first to a second position when and only when energ fiows through the relay winding from its second to its first terminal, a coding device having a contact continuously actuated between a first and a second position, said coding device contact being effective when in its first position to connect a track battery across said section rails in multiple with the winding of said detector relay with the positive terminal of said battery connected to said first track rail, and mean operative on movement of the contacts f said track relay to their first position to momentarily connect a feed back battery across said section rails in multiple with the winding of said track relay with the positive terminal of said battery connected to said second track rail, the circuits over which energy is supplied from the track battery to the detector relay winding and from the feed back battery to the track relay being of relatively high inductance so that on interruption of the circuit of the battery associated with each of these relays energy continues to fiow temporarily in the circuit of the relay and prevents operation of the relay by energy supplied thereto due to inductive discharge of the track circuit on interruption of the circuit of the battery associated with each of these relays.

13. In a coded railway signaling system, in combination, a section of railway track having a first and a second track rail, a code following track relay at one end of the track section having its winding connected across the section rails with the first terminal of the relay winding connected to the first rail and the second terminal of the relay Winding connected to the second rail, said track relay having a contact biased to a released position and movable therefrom to a picked-up position when and only when energy fiows through the relay winding from the first to the second terminal thereof, means operative on movement of the contacts of said track relay to their'released position to momentarily connect a feed back battery across the section rails and the winding of said track relay in multiple with the positive terminal of the battery connected to the second track rail, the circuit over which energy i supplied from the feed back battery to the track relay being of relatively high inductance so that on interruption of the circuit of the feed back battery energy continues to fiow temporarily in the circuit of the track relay winding from the second to the first terminal thereof and is of such magnitude as to prevent operation of the relay by energy supplied thereto due to the inductive discharge of the track circuit occurring on interruption of the circuit of the feed back battery, a feed back detector relay at the other end of the track section, means for connecting the winding of said detector relay across the section rails, and a coding device located at said other end of said track section and having a contact continuously actuated between a first and a second position, said coding device contact being effective when in its first position to connect a track battery across the section rails with the positive terminal of the battery connected to said first track rail.

14. In a coded railway signaling system, in combination, a section of railway track having a first and a second track rail, a code following track relay at one end of said track section having its winding connected across the section rails, a code following detector relay at the other end of said track section having its winding connected across the section rails in series with a reactor, said detector relay being of a type the contacts of which are moved from a first to a second position when and only when energy flows through the relay winding in a given direction, a coding device having a contact continuously actuated between a first and a second position, said contact being effective when in its first position to connect a track battery across the section rails in multiple with said reactor and the detector relay winding in such manner that energy from said track battery flows through the winding of said detector relay in the reverse of said given direction, said reactor being proportioned so that on interruption of the circuit of the track battery energy supplied from the reactor to the detector relay prevents operation of the detector relay by energy supplied thereto due to inductive discharge of the track circuit occurring on interruption of the circuit of the track battery, said coding device contact being efiective 

